There has long been a need for inexpensive chainstoppers that can be derived from standard intermediates, such, for example, as [(CH.sub.3).sub.2 SiO].sub.4 and [CF.sub.3 (CH.sub.2).sub.2 Si(CH.sub.3)O].sub.3, and which can be produced through equilibration and with the use of a readily available catalyst such as potassium hydroxide. Such a chainstopper is desirable for use in the production of vinyl-stopped fluorosilicone polydimethylsiloxane copolymer compositions. Additionally, it is applicable in the reworking of certain out-of-specification low energy molding (LEM) copolymers wherein, for example, the mole percent fluorosilicone content may be too low, where vinyl end groups may need to be re-established, or where the viscosity must be reduced for a particular application.
Applicant has provided a fluorosilicone polydimethylsiloxane equilibration chainstopper and process for making same which involves the manufacture of a fluorosilicone chainstopper having a fluorosilicone content in a range which particularly adapts the chainstopper for the above-discussed purposes.
More particularly, the primary object of this invention is to provide a novel fluorosilicone polydimethylsiloxane chainstopper having a mole percent fluorosilicone content which especially adapts it for use in producing low energy molding copolymers.
Another object is to provide a new and improved fluorosilicone chainstopper which is readily prepared with the use of standard intermediates and thus enables selection of materials from a broader base of usable starting materials and enables reduced production costs.
An additional object is to provide a fluorosilicone polydimethylsiloxane chainstopper especially effective in the preparation of high fluorosilicone content copolymer fluids.
Yet another object is to provide a new and improved fluorosilicone polydimethylsiloxane chainstopper useful for reducing the molecular weight of high molecular weight copolymers and for re-establishing vinyl-end groups on copolymer chains. A common source of such materials would be out-of-specification copolymers characterized by the absence of essential vinyl-end groups and reduced density which characteristics ordinarily render the out-of-specification copolymers unsatisfactory as base components for low energy molding systems.
The objects of the present invention are met by a fluorosilicone polydimethylsiloxane having a fluorosilicone content within the rane of 30 mole percent to 60 mole percent and the following formula: ##STR1## in which R.sub.F is CF.sub.3 CH.sub.2 CH.sub.2 --, X is approximately, 10 to 30 and Y is approximately, 20 to 50.
By way of further discussion of the background of the present invention and in order to facilitate understanding of the invention, it is to be noted that in the preparation of low energy molding (LEM) compositions, that is, higher molecular weight copolymers which are used to make heat cured silicone rubbers by means of copolymerization, the particular chainstopper selected for use in terminating the copolymerization process is often determined by the polymerization process to be used. Other factors considered in making the determination are the viscosity desired for the end product, the desired molecular weight of the end product and the preferred mole percent fluorosilicone content of the copolymers being produced.
Copolymers which may be effectively produced with the present invention find utility, for example, in common applications such as in solvent resistant transparent tubing, and in electrical cable receptacle pin sealants and in sealants for aircraft fuel lines. Additionally, such copolymers are often formulated to have a fluorosilicone content of at least 50 mole percent in order to afford a high degree of resistance to aromatic solvents, such as toluene and JP-4 fuel while still maintaining their physical integrity over a temperature range of, for example, -75.degree. C. to +100.degree. C. Furthermore, fluorosilicone polydimethylsiloxane chainstoppers are often used in the preparation of low viscosity (300-1000 centipoise) copolymer and terpolymer fluids to serve as the base for polytetrafluoroethylene (PTFE) containing greases.